x86, mm: Allow ZONE_DMA to be configurable (dc382fd5) · Commits · 戴 / test

ZONE_DMA is unnecessary for a large number of machines that do not require less than 32-bit DMA addressing, e.g. ISA legacy DMA or PCI cards with a restricted DMA address mask. This patch allows users to disable ZONE_DMA for x86 if they know they will not be using such devices with their kernel. This prevents the VM from unnecessarily reserving a ratio of memory (defaulting to 1/256th of system capacity) with lowmem_reserve_ratio for such allocations when it will never be used. Signed-off-by:

David Rientjes <rientjes@google.com> Link: http://lkml.kernel.org/r/alpine.DEB.2.00.1105161353560.4353@chino.kir.corp.google.com Signed-off-by:

H. Peter Anvin <hpa@linux.intel.com>

arch/x86/Kconfig

+8 −1

Original line number	Diff line number	Diff line
		@@ -112,7 +112,14 @@ config MMU
		def_bool y

		config ZONE_DMA
		def_bool y
		bool "DMA memory allocation support" if EXPERT
		default y
		help
		DMA memory allocation support allows devices with less than 32-bit
		addressing to allocate within the first 16MB of address space.
		Disable if no such devices will be used.

		If unsure, say Y.

		config SBUS
		bool

arch/x86/mm/init_32.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -678,8 +678,10 @@ static void __init zone_sizes_init(void)
		{
		unsigned long max_zone_pfns[MAX_NR_ZONES];
		memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
		#ifdef CONFIG_ZONE_DMA
		max_zone_pfns[ZONE_DMA] =
		virt_to_phys((char *)MAX_DMA_ADDRESS) >> PAGE_SHIFT;
		#endif
		max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
		#ifdef CONFIG_HIGHMEM
		max_zone_pfns[ZONE_HIGHMEM] = highend_pfn;

arch/x86/mm/init_64.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -616,7 +616,9 @@ void __init paging_init(void)
		unsigned long max_zone_pfns[MAX_NR_ZONES];

		memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
		#ifdef CONFIG_ZONE_DMA
		max_zone_pfns[ZONE_DMA] = MAX_DMA_PFN;
		#endif
		max_zone_pfns[ZONE_DMA32] = MAX_DMA32_PFN;
		max_zone_pfns[ZONE_NORMAL] = max_pfn;

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